Sender:

In the communication process, sender is the individual who initiates a message.And is also called the communicator or source of communication. 

For example,A sender is the person who put a letter in the mailbox. Also known as a source or a transmitter, a sender is a device that originates, or generates, an information transfer to one or more receivers. 

Receiver:

The individual or the group of individuals who responds to the sender is called the receiver or audience.

For example, in electronics, any of various devices that accept signals, such as radio waves, and convert them (frequently with amplification) into a useful form. Examples are telephone receivers, which transform electrical impulses into audio signals, and radio or television receivers, which accept electromagnetic waves and convert them into sound or television pictures.